Weak Sequencing (Combined Fragment)   A weak sequencing interaction operator (signified by the value of seq) defines a combined fragment where the order of event occurrences within one operand are significant and event occurrences on different lifelines can be interleaved, but event occurrences on the same lifeline, in different operands must occur in the order of the operands. Thus event occurrences in the first operand must occur before event occurrences in the second operand if they are on the same lifeline.

Explanation

Weak sequencing is a way of defining a relationship between a number of traces enclosed within the fragment. It is a hybrid operator allowing for traces to be interleaved between unrelated lifelines but requires the traces to be executed in sequence when they are on the same lifeline. When the event occurrences are on the same lifeline and within a single operand they must be executed in order. When event occurrences are in different operands but involve the same lifeline the traces of the first operand must be executed before the second and the second before the third and so on.

Related Entries

Strict Sequencing (Combined Fragment)  Graphically Similar A combined fragment with an operator of strict sequencing (strict) is related to a combined fragment with an operator of weak sequencing (seq) because when weak sequencing applies to a single participant it is semantically equivalent to strict sequencing.

Parallel (Combined Fragment)  Graphically Similar A combined fragment with an operator of parallel (par) is related to a combined fragment with an operator of weak sequencing (seq) because when the operands apply to different (disjoint) participants then it is semantically equivalent to a parallel merge.